The present invention relates to a water purification device and, more particularly, to a low-cost device that is portable and avoids the need for using pressure recovery but instead using a straightforward flow path by way of back pressure regulation.
A typical reverse osmosis (RO) water purification system uses a high-pressure pump to provide high pressure raw water at a steady flow rate to the membrane element or elements. Almost all small to medium size reverse osmosis systems use spiral wound membrane elements. These cross-flow elements have one inlet stream and two outlet streams, more specifically, a feed fluid inlet opening, a retentate outlet and a permeate outlet. The permeate outlet is isolated from the retentate outlet and from the inlet. This type of spiral wound membrane is described in U.S. Pat. No. 3,367,504 which sets forth a method and apparatus for recovering purified water from sea water by applying the (RO) principle and employing a spirally wound modular membrane.
Although small, handheld RO devices that allow for implementation of spiral wound membranes are also known, they typically feature an elaborate system of plumbing to allow for pressure recovery which is the process of converting the pressure energy of the discharge brine stream into useful energy. These energy recovery devices are also effectively implemented in many large steady flow RO systems. However, in such small hand operated devices, pressure recovery mechanisms marginally increase the system efficiency and lead to overly complex devices such as that outlined in U.S. Pat. No. 4,187,173 which can not be implemented effectively in an actual device.
A significant effort has been spent on improving the performance of RO membranes and their configuration. U.S. Pat. No. 3,367,504 describes an RO separation apparatus employing an envelope of semi-permeable membrane sheets spaced apart by a layer of porous backing material and spirally wound with a continuous length of separator grid material about a hollow mandrel. An aqueous feed solution is introduced through the separator grid material, permeated water passes through the membranes and into the backing material by reverse osmosis and the backing material discharges the permeated water into the hollow porous mandrel.
U.S. Pat. No. 6,632,357 discloses another configuration for the RO membrane which includes a laminated composition having two sheets formed from a polymer and positioned adjacent one another to form a fluid passage there between. The outside surfaces of the sheets are permeable to allow fluid flow from the outside surface to the fluid passage. The outside surface and of the laminated composition includes a plurality of embossed islands spaced from one another to define feed pathways around and between the embossed islands.
U.S. Pat. No. 3,365,061 discusses a portable apparatus for producing desalinized water. A hand-operated reciprocating piston pump supplies saline water through a check valve into a line connected to a reverse osmosis purification device. A hydraulic accumulator is connected to the line through an initially closed valve which opens when pressure in the line is at a value above the osmotic pressure of the aqueous solution. A relief valve prevents rupture of the semi-permeable membranes and throttle valve in the discharge line facilitates maintenance of the desired operating pressure.
U.S. Pat. No. 4,070,280 describes an RO apparatus using a pump for pressurizing feed water introduced into a pressure resistant container in which is slidably mounted a semi-permeable membrane cartridge. This membrane cartridge contains an inner passage for the collection of purified water; the movement of the membrane cartridge inside the pressure resistant container provides “a very high degree of turbulence in the fluid flowing over the membrane stroke.” This device contains an inlet for contaminated water, and outlet for concentrated contaminated water and a second outlet for purified water.
In the aforementioned known RO apparatus, the purified water flows from the center of the membrane, through the rod (“attached to an end of the semi-permeable membrane cartridge, and passes slidably and sealingly through one end of the pressure resistant container”) and into a purified water container. This hollow rod is connected to means for reciprocal actuation as well as an outlet container for accumulating the purified water. The actuation of the membrane provides “improved turbulence and circulation of the feed water through the semi-permeable membrane cartridge over the membrane surfaces. The common means may be in the form of a lever operated by a handle or pedal, or by a power source such as an electric motor.” This motion of the semi-permeable membrane is not to pressurize one end of the pressure resistant chamber so as to force purified water into the core of the membrane; the pressurization necessary to force water into the core of the membrane is performed by the external pump.
U.S. Pat. No. 4,187,173 discloses a device where water desalination is achieved by using a semi-permeable membrane which selectively permeate purified water from a feed solution pressurized by reciprocating piston or diaphragm pump. Pump action is assisted by returning pressurized concentrate fluid acting on the reverse side of the pump or diaphragm. Directional valves controlling alternating admission and venting of concentrate fluid to and from pump cylinder are actuated mechanically by reversal force applied to the piston rod.
In a conventional, steady flow RO system, high-pressure salt water is supplied to a commercial membrane, and a small fraction of this water passes through the membrane becoming potable desalinated drinking water, while the remaining water is discharged as brine. Similarly, in conventional individual RO water purifiers, as described in U.S. Pat. No. 4,187,173, a fixed flow is passed through the membrane with each stroke.
Current commercial configurations follow the design disclosed in U.S. Pat. No. 4,187,173 where a flow valve directs the discharge of the pump (generated on the front side of the piston) into the membrane. Additionally, the high pressure brine is brought to the backside of the piston in an attempt to recover its pressure energy. To discard this brine a flow valve directs the brine out of the device during the piston upstroke. This type of configuration, while being unduly complex and costly also requires significant pumping effort on both the upstroke and down stroke of the piston. A significant amount of effort is required when one considers that this pump must be actuated approximately 30 stokes per minute. In addition, proper implementation of the pressure recovery requires that the high pressure brine be removed from the outlet end of the membrane, thus allowing it to properly operate as a cross flow device. This cannot be effectively implemented, however, in a device with a removable pressure vessel that allows membrane replacement.
Current commercial devices which are based on U.S. Pat. No. 4,187,173 short circuit the cross-flow membrane by taking high pressure water from the inlet side of the membrane which is detrimental to membrane performance and life. The intermittent configuration disclosed here is a radical departure from the configuration disclosed in U.S. Pat. No. 4,187,173 and used by commercial individual water purifiers. While energy recovery is beneficial for large continuously flowing systems, it provides no practical value in this individual water purification application.